doc: fix table markup in previous commit

"These "border lines" need to have a length higher or equal to the
longest line in the table that would be generated, so you'll have
to update them as well." - narfbg
diff --git a/user_guide_src/source/libraries/form_validation.rst b/user_guide_src/source/libraries/form_validation.rst
index bab61f1..ce1695d 100644
--- a/user_guide_src/source/libraries/form_validation.rst
+++ b/user_guide_src/source/libraries/form_validation.rst
@@ -911,15 +911,15 @@
 The following is a list of all the prepping methods that are available
 to use:
 
-==================== ========= ===================================================================================================
+==================== ========= =======================================================================================================
 Name                 Parameter Description
-==================== ========= ===================================================================================================
+==================== ========= =======================================================================================================
 **xss_clean**        No        Runs the data through the XSS filtering method, described in the :doc:`Security Class <security>` page.
 **prep_for_form**    No        Converts special characters so that HTML data can be shown in a form field without breaking it.
 **prep_url**         No        Adds "\http://" to URLs if missing.
 **strip_image_tags** No        Strips the HTML from image tags leaving the raw URL.
 **encode_php_tags**  No        Converts PHP tags to entities.
-==================== ========= ===================================================================================================
+==================== ========= =======================================================================================================
 
 .. note:: You can also use any native PHP functions that permits one
 	parameter, like ``trim()``, ``htmlspecialchars()``, ``urldecode()``,